The phacoemulsification apparatus is used in eye surgery for removing the natural crystalline lens of the eye. The conventional phacoemulsification apparatus includes a hand piece having an ultrasonic transducer for driving a hollow phacoemulsification needle. The hand piece is provided with an irrigation line and an aspiration line, and is configured for directing the flow of irrigation fluid through the needle into the eye. The hand piece is also provided with a sleeve surrounding the phacoemulsification needle, and is further configured for aspirating fluid to flow from the eye into a lumen defined between the needle and sleeve.
During cataract surgery, a small incision is made in the eye and the hand piece is manipulated so that the phacoemulsification needle with the sleeve is inserted through the small incision. After capsulorrhexis, the ultrasonically driven phacoemulsification needle is placed in contact or near contact with the cateracteous natural lens or lens nucleus and vibrated ultrasonically to begin erosion of the structure of the lens nucleus. As the structure of the lens nucleus is destroyed, the lens debris is vacuumed into the needle cannula, through the hand piece, and then out of the hand piece through the aspiration line.
During the phacoemulsification process, the ultrasound energy applied to the lens nucleus by the phacoemulsification needles creates a repulsive force which tends to push free-floating fragments away from the tip of the phacoemulsification needle. The aspiration line connected to the hand piece provides aspiration or "flow" that draws fluid into the tip of the phacoemulsification needle via a pump (e.g. peristaltic pump, venturi, vacuum pump, etc., or combinations thereof), and overcomes the repulsive force to some extent. However, there is still observed many instanes where nuclear fragments are "pushed" away from the tip of the phacoemulsification needle.
The conventional phacoemulsification apparatus includes a source for irrigation fluid (e.g. one or more bottles of irrigation fluid) and a source of vacuum (e.g. peristaltic pump, venturi, vacuum pump, etc., or combinations thereof). The conventional phacoemulsification apparatus also includes a power supply and control for driving the ultrasonic hand piece, and thus the tip of the phacoemulsification needle. Typically, the conventional phacoemulsification apparatus includes a console containing the power supply, control (e.g. analog and/or microprocessor), peristaltic pump, and other components. The hand piece is electrically connected to the hand piece by a cable, and fluidly connected to the irrigation fluid supply and vacuum source by a tubing set.
The conventional phacoemulsification apparatus has electronics configured for driving the ultrasonic hand piece at different power levels based on the position on a foot pedal control. Some conventional phacoemulsification apparatus are configured for providing a "pulse mode" believed to be effective for breaking up the lens nucleus more effectively. However, in the conventional "pulse mode", the pulses are constant. Specifically, the pulses achieve approximately the same power level, the same pulse width or duty cycle, and the pulses are equally spaced apart timewise.
To minimize the "pushing" or repulsive effect of ultrasound waves propagating from the tip of the phacoemulsification needle on the nuclear fragments, the "pulse-mode" was created to energize the ultrasonic hand piece, and thus tip of the phacoemulsification tip intermittently. Accordingly, the repulsive force effect is only applied intermittently, allowing the aspiration (flow) rate to keep the free nuclear fragment(s) closer to the ultrasound tip for quicker removal. However, repulsion of a nuclear fragment is still frequently noted even with operation of the pulse-mode, especially when the pulse-rate is high. Low pulse-rates have been used to enhance prevention of occlusions with some success, but the prevention of enhanced occlusions is counterproductive to certain techniques of phacoemulsification.
Further, the conventional single setting pulse-mode, such as six (6) pulses per second, sets up standing waves relative to the tip of the phacoemulsification needle, which negates the desired effect of pulse-mode. These standing wave create not only ultrasound repulsions, but fluid repulsion as well, thereby further hindering efficient nuclear removal.
To maximize the proximity of free nuclear fragments to the phacoemulsification tip and thereby improve the speed and efficiency of phacoemulsification, new innovations to the conventional pulse mode are needed.